1. Field of Invention
This invention relates to the field of nuclear medicine, and in particular to nuclear medicine imaging systems, and the control of their quality.
2. Description of the Related Art
Nuclear medicine is a unique medical specialty wherein radiation is used to acquire images that show the function and anatomy of organs, bones or tissues of the body. Radiopharmaceuticals are introduced into the body, either by injection or ingestion, and are attracted to specific organs, bones or tissues of interest. Such radiopharmaceuticals produce gamma photon emissions that emanate from the body. One or more detectors are used to detect the emitted gamma photons, and the information collected from the detector(s) is processed to calculate the position of origin of the emitted photon from the source (i.e., the body organ or tissue under study). The accumulation of a large number of emitted gamma positions allows an image of the organ or tissue under study to be displayed.
Proper imaging requires that the camera be calibrated to eliminate or minimize distortions. Such distortions can be caused, for example, by lack of a uniform response to incident radiation over the entire area of the scintillation detector surface, by non-linear responses to incident radiation by different photomultiplier tubes arrayed over the scintillation crystal, and by variations in the energy window defining the range of photon energy levels of a scintillation interaction or “event” that will be accepted as contributing to the image.
Routine quality control of a nuclear imaging system may require the provision of a variety of radioactive sources. The sources are used as baselines to calibrate the camera. The sources may be required to be provided in a variety of configurations, such as a 57Co sheet source and a variety of 99 μTc point and line sources. Furthermore, the point and line sources may need to be prepared on site.
A camera may need to be “peaked” daily before switching to a new radio nuclide to ensure that the energy window is correct. Uniformity may need to be checked daily as well, using a high count flood. In a high count flood, a collimator may be removed and a point source, such as a 57Co disc source or a water-filled phantom may be viewed from a distance of five times the diameter of the detector. A water filled phantom may need to be prepared on site. Camera uniformity may need to be checked weekly.